1. Field of the Invention
The invention relates to the acid dyeing of polyamide fibers and fabrics made therefrom.
2. Prior Art
The dyestuffs used in the process according to the invention are known materials and are described in U.S. Pat. No. 3,485,572 as well as in West German Pat. No. 1,932,828, published Jan. 7, 1971.
The present invention relates to the use of the known yellow dyestuff having the formula: ##STR2## wherein X, Y and the COOH group configuration are as defined above, for dyeing polyamide fibers. These dyestuffs are scarcely water-soluble, are free of sulphonic groups and have a carboxylic acid chain.
As is known, one of the typical characteristics of artificial and chemical fibers is the good dyeability of the articles manufactured therefrom. In the field of polyamide fibers in particular, perfectly uniform dyeing are difficult to obtain, since variations of physical or chemical nature inherent in the fiber substantially affect the tinctorial uniformity. The tinctorial defects which result are usually called "streaks" or barrinesses.
Generally, a dyeing is required to exhibit uniformity and good stability characteristics. These two properties, apart from the fastness to light, are not always simultaneously provided by a given dyestuff, especially with regard to polyamide fibers; indeed, in this connection it might even be said that the faster a dyestuff, the less equalizing or levelling is the dyeing and vice-versa.
For these fibers, and in particular for polyamides, dispersed and anionic dyes, suitably selected for obtaining well defined shades (yellow in the present case) are generally employed. The dispersed dyes (e.g. Microsetile -- ACNA) may be usefully employed for obtaining pale color shades, as they possess a high equalizing power with respect to coverage of streaks in the fibers being dyes. When preparing dyeings of middle or full color shades, what must be borne in mind (in addition to the practical impossibility of obtaining very intense shades with these dyestuffs) is the low stability of these dyeings to wet-treatments.
Selected anionic dyestuffs (e.g. Nailamide -- ACNA) offer good possibilities for obtaining dark color shades, scarce possibilities for middle color shades, and they are generally unsuited for providing pale color shades owing to their insufficient equalizing power.
The use of auxiliary agents of the anion-active type (e.g. Dispergal FP Trademark of a Montedison product), cation-active type (e.g. Dispersol CWL Trademark of a Montedison product) or non-ionic type when effecting the dyeing, leads to some improvements for the middle color shades, but well-equalized pale shades are never quite obtainable when using these dyestuffs, even with said auxiliary agents.